Spatially controlled fabrication of single NV centers in IIa HPHT diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2019-12-23 |
| Journal | Optical Materials Express |
| Authors | Sergei D. Trofimov, Sergey A. Tarelkin, Stepan V. Bolshedvorskii, Vitaly S. Bormashov, Sergey Yu. Troshchiev |
| Citations | 28 |
| Analysis | Full AI Review Included |
Spatially Controlled Single NV Center Fabrication in Low-Nitrogen Diamond
Section titled âSpatially Controlled Single NV Center Fabrication in Low-Nitrogen DiamondâExecutive Summary
Section titled âExecutive SummaryâThis documentation analyzes the technical feasibility and material requirements for the spatially controlled fabrication of single Nitrogen-Vacancy (NV) centers in diamond, a crucial step for quantum photonics applications. The research validates a vacancy-driven technique using helium ion (4He+) implantation into low-nitrogen High-Pressure/High-Temperature (HPHT) diamond.
| Material Requirement Analysis | 6CCVD Advantage |
|---|---|
| Material Purity: Success relies heavily on ultra-low residual nitrogen concentration (specifically < 50 ppb) found in the {001} growth sector. | 6CCVDâs MPCVD Single Crystal Diamond (SCD) inherently achieves ultra-low nitrogen content (often < 1 ppb), offering superior baseline purity for high-fidelity NV creation. |
| NV Fidelity: Single NV centers were reliably created in the {001} growth sector, while the higher nitrogen {111} sector resulted in undesirable NV clusters. | 6CCVD provides high-quality, high-purity SCD wafers optimized for the critical {001} orientation. |
| Coherence Time (T2*): Achieved T2* up to 321 ns, with the potential for massive improvement using isotopically purified 12C diamond. | 6CCVD specializes in Isotopically Purified 12C SCD, the industry standard for maximizing T2* (coherence times). |
| Fabrication Method: Requires complex processes including precise lithography, ion implantation (50 keV), vacuum annealing (700 °C), and surface metalization for markers. | 6CCVD offers custom SCD wafers with necessary services, including Ra < 1nm polishing, high-precision laser cutting, and custom Au/Pt/Ti metalization. |
| Target Application: Single photon sources, quantum registers, and nanoscale magnetic field detectors. | 6CCVD materials support these advanced quantum and sensing technologies globally. |
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal Ion Energy | 50 | keV | Helium (4He+) Implantation |
| Optimal Ion Dose | 1.0 x 1010 (or 100) | ions/cm2 (or ions/”m2) | For creating groups of single NVs |
| Target NV Depth | ~250 (or 0.3) | nm (or ”m) | Optimized for Solid Immersion Lenses (SIL) / Waveguides |
| Annealing Temperature | 700 | °C | Required for vacancy migration and NV formation |
| Annealing Environment | Vacuum | N/A | High temperature post-implantation processing |
| Nitrogen Concentration ({001} GS) | < 1.0 x 1016 (< 50) | cm-3 (ppb) | Ultra-low residual N content required for single NVs |
| Nitrogen Concentration ({111} GS) | ~ 1.0 x 1017 (~500) | cm-3 (ppb) | High N content resulting in NV clusters |
| NV Spin Relaxation Time (T2*) ({001}) | 321 | ns | Measured via Optically Detected Magnetic Resonance (ODMR) |
| NV Spin Relaxation Time (T2*) ({111}) | 254 | ns | Lower T2* attributed to higher N concentration |
| Intrinsic Dephasing Rate ($\delta \nu_{MW=0}$) ({001}) | 0.99 | MHz | Used to calculate T2* |
| Positioning Accuracy | 0.5 | ”m | Limited by vacancy migration during annealing |
| Sample Polishing Requirement | Ra < 5 | nm | Used for mechanical preparation |
| Hardmask Material/Thickness | Nickel (Ni) / 400 | nm | Used for ion implantation patterning |
Key Methodologies
Section titled âKey MethodologiesâThe NV center creation relies on a precise vacancy-driven scheme utilizing low-nitrogen HPHT Type IIa diamond.
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Material Growth (HPHT Simulation):
- Method: Temperature Gradient High-Pressure High-Temperature (TG-HPHT).
- Conditions: High pressure (5 GPa) and high temperature (~ 1750 K).
- Purity Control: Fe-Al-C alloy used as a solvent, with Aluminum (Al) acting as a nitrogen getter to produce colorless Type IIa diamond.
- Preparation: Diamond plate laser-cut to (111) orientation and mechanically polished to Ra < 5 nm.
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Surface Preparation and Mask Fabrication:
- Coordinate Markers: Temperature-resistant coordinate markers etched into the diamond surface using Reactive Ion Etching (RIE) in SF6 plasma.
- Metal Grid: A metal coordinate grid (100 ”m x 100 ”m squares, 10 ”m line width) fabricated via lift-off photolithography and magnetron sputtering for initial NV search and focusing.
- Hardmask: A 400 nm thick Nickel (Ni) mask was patterned using lithography, featuring circle holes ranging from 0.5 ”m to 19.5 ”m in diameter.
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NV Center Creation (Vacancy-Driven):
- Implantation: 4He+ ions implanted through the hardmask holes at 50 keV and a dose of 1010 ions/cm2 to create local vacancies at a depth peak of ~250 nm.
- Cleaning: Hardmasks and the initial metal grid were removed in aqua regia.
- Annealing: The sample was annealed in vacuum at 700 °C. This heat treatment induces vacancy migration and merging with residual substitutional nitrogen (Ns) impurities to form the desired NV centers (NV-).
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Characterization:
- Location/Intensity: Luminescence mapping using a confocal microscope with a 532 nm laser to visualize NV center distribution and intensity (636-641 nm range).
- Single NV Confirmation: Home-built confocal microscope system and Hanbury-Brown-Twiss (HBT) interferometer were used to measure the second-order photon correlation function g(2)(t). Antibunching (g(2)(0) approaching zero) confirms single NV centers.
- Coherence Time: Optically Detected Magnetic Resonance (ODMR) measured the intrinsic dephasing rate ($\delta \nu_{MW=0}$) to determine the inhomogeneous spin relaxation time (T2*).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the foundational SCD materials necessary to replicate, simplify, and significantly advance the research demonstrated in this paper, particularly regarding spin coherence and NV yield fidelity.
Applicable Materials
Section titled âApplicable MaterialsâThe success of the vacancy-driven technique hinges on ultra-low nitrogen content and superior crystal quality, which are intrinsic properties of 6CCVDâs MPCVD SCD.
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Optical Grade SCD (Low-Nitrogen, High-Purity):
- Requirement Match: The paper confirmed the necessity of ultra-low nitrogen ([N] < 50 ppb) for single NV fabrication. 6CCVDâs MPCVD SCD wafers offer nitrogen concentrations often < 1 ppb, providing an inherently purer environment than the low-nitrogen HPHT {001} sector, reducing background intrinsic NV noise (1010 cm-3 in the paper) and preventing clustering.
- Orientation Control: We supply custom SCD substrates oriented to the critical {001} plane required for high-fidelity single NV formation.
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Isotopically Purified 12C SCD:
- Performance Enhancement: The research explicitly notes that T2* (321 ns) can be further improved using isotopically purified 12C HPHT diamond. 6CCVDâs MPCVD process is optimized for isotopic engineering. Using 6CCVDâs > 99.999% 12C SCD would dramatically suppress nuclear spin bath decoherence, potentially increasing T2* by an order of magnitude, crucial for quantum processing and memory applications.
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Single Crystal Diamond Substrates (Up to 10 mm thick):
- We offer substrates for thermal and mechanical stability needed during high-temperature annealing (700 °C) and subsequent processing steps (etching, metalization).
Customization Potential
Section titled âCustomization Potentialâ6CCVD provides end-to-end processing capabilities essential for replicating and optimizing the advanced fabrication sequence used in this research.
| Service Category | 6CCVD Capability | Research Application Alignment |
|---|---|---|
| Custom Dimensions | Plates/wafers up to 125mm (PCD). Custom laser cutting available for small, application-specific chips. | Replication of experimental sample sizes and precise microstructuring. |
| Surface Engineering | Polishing to Ra < 1nm (SCD). Superior surface quality compared to the Ra < 5 nm used in the paper, improving lithography and minimizing surface defects impacting NV quantum properties (as noted in Ref. [22]). | Essential for defining precise hardmasks and waveguiding structures (SIL overgrowth). |
| Custom Metalization | Full in-house capability for standard metal stacks including Ti, Pt, Au, Pd, W, and Cu. | Fabrication of temperature-resistant metal coordinate markers and hardmasks (Nickel/Ti/Pt/Au variations) via magnetron sputtering/e-beam deposition. |
| Thickness Control | SCD layers from 0.1 ”m up to 500 ”m. | Allows precise control over the bulk diamond properties and enables fabrication of required thin layers (e.g., 500 nm waveguides) post-implantation. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team provides specialized consultation to engineers and scientists seeking to transition from research-grade HPHT materials to high-performance MPCVD SCD. We specialize in optimizing material selection and preparation parameters for single NV center creation, quantum registers, and high-coherence magnetic sensing projects. We assist in defining optimal specifications, including isotopic purity, orientation, and surface termination, necessary to maximize T2* coherence times and device yield.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Single NV centers in HPHT IIa diamond are fabricated by helium implantation through lithographic masks. The concentrations of created NV centers in different growth sectors of HPHT are compared quantitatively. It is shown that the purest {001} growth sector (GS) of HPHT diamond allows to create groups of single NV centers in predetermined locations. The {001} GS HPHT diamond is thus considered a good material for applications that involve single NV centers.